Preventing mould from coming back on bathroom ceiling

Maybe someone can help? We have a recurrent problem with brown mould spots appearing on our bathroom ceiling above the shower cubicle. They rub off easily with Cif but keep coming back.

I don't know why as the bathroom has two ventilators (VCM? They go up into the loft - one is beside the shower and the other is at the other side of the room) and a large Velux window. The window is always open when we shower and left open to air afterwards. I often keep the door open as well so it is not a question of lack of 'airing'.

We have had the loft checked and it is well insulated.

Someone suggested it may be because the bathroom is too cold - we have a heated towel rail otherwise no heating in what is a fairly large room (separate bath and shower cubicle, sink and toilet area (separated by a wall). Or that the paint was not suitable for bathrooms.

It is just the area above the shower cubicle which is affected.

We will redecorate this room soon - what can I do to minimise the risk of mould reappearing bar using special bathroom paint? TIA.

We make sure we open the window daily, even when it's voluntary so that the room is aired and the steam from the shower can escape. We also use bathroom paint. We have had small patches of mould in the past and bleached them area using an old toothbrush and they never came back.

Polter they are not extractor fans so they must be vents. The one above the shower gets very dusty and dirty so I assume it must be working. I dare not shower with the the window and door shut - it would be a veritable steam room!!!!